Abstract
In present study, we measured the Total Electron Content (TEC) variation in the ionosphere from Global Navigation Satellite System (GNSS) data which might have been induced by earthquakes in the Himalayan region. The results were analysed with other inducing factors (geomagnetic storm and solar flare) affecting TEC in order to constraint the causative factor. The study has been performed to understand a relationship between ionospheric electron content and earthquakes occurrences with special emphasis on Himalayan region and provides information on spatio-temporal variation of TEC from GNSS observation stations vis-à-vis prominent earthquakes of the region. The results indicate that the ground based GNSS (GPS) observations show the deviation in vertical total electron content (vTEC) in ionosphere few days prior to the seismic event as evident from our two continuously operating reference stations (CORS) as well as from CORS of UNAVCO data centre. Ionospheric perturbation has also been observed in case of low magnitude earthquakes (Mw 4.9 in present study) whenever recording station lies very close to the epicentre. TEC variation is found to increase as the epicentre distances decreases. In case of Mw 7.8, 2015 Nepal earthquake the TEC variation is found to increase by 15–20 TEC unit recorded at station separated by 60 km apart. This may provide us the avenue for epicentre detection as TEC concentration was found to increase as we move closer to the epicentre. TEC variations (mostly high TEC) have been observed during a period of 0–8 days prior to 4 earthquakes: 1st April 2015 Pipalkoti earthquake (4.9Mw), 25th April 2015 Nepal earthquake (7.8Mw), 26 April 2015 (6.7Mw) and 12th May 2015 (7.3Mw) Nepal earthquakes. Significant low TEC values were also observed before 13–14 days prior to first two earthquake events. Overall the study has revealed that low TEC followed by couple of high TEC values correlate well with the seismic events in Himalayan region.
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